"The Geological Survey is conducting an analysis of the distribution and formation of manganese nodules in the Gulf of Finland, which was one of the main objectives of our [expedition]," Sten Suuroja, head of the department of marine geology and geophysics at Geological Survey of Estonia, explained in the "Vikerhommik" radio program.

Polymetallic nodules, commonly known as manganese nodules, are seafloor mineral concretions composed of layers of iron and manganese hydroxides surrounding a core. The majority of nodules are 3 to 10 centimeters in diameter, around the size of hen's eggs or potatoes.

Suuroja said that studying manganese nodules is important for two reasons. First, they play a key function in the ecological cycle of the seafloor, and the geologist also explained their economic significance: "Increasing number of people are exploring the deep sea bedrock for mineral resources. As the name suggests, there is actually manganese there, which belongs to the class of accumulator metals," he explained. So the metals they contain are the ones we need to transition to renewable energy and other green technologies.

Whether the bottom of the Gulf of Finland could become a source of revenue is still to be determined by the international working group.

The British Natural History Museum reported that the only technology existing to collect the nodules in the deep sea would be tractor-sized machines that "crawl along the bottom, collecting the nodules and sending them back to the surface via a kilometers-long tube as they go." However, the maximum depth of the Gulf of Finland is only 115 meters.

Freshwater flowing underground below the seafloor

Aivo Lepland of the Norwegian Geological Survey, the project's primary coordinator, said that in addition to the nodules, the scientists saw large holes in the seafloor in the middle of the Gulf of Finland. "They range from a few dozen to a few hundred meters in diameter and are up to three meters deep. The holes are caused by groundwater rising from the bottom of the sea and causing changes in the seabed," he said.

According to Lepland, it will be fascinating to study these seafloor "craters" as well, as they are home to unique colonies of microorganisms. "Now, we are attempting to study the interaction of all these factors: the nodules, the processes on the seafloor, where the [freshwater] water comes out, and the biological aspect associated with it — what microbes do in relation to these processes," he went on to explain.

The recently completed expedition was part of a wider project involving scientists from Poland, Norway, Sweden, Finland and Estonia on the topic of groundwater leakages to the seabed.

According to Suuroja, marine scientists are diligently at work and their analysis of the collected samples is far from complete: a preliminary picture requires a thorough geochemical and biological investigation. "Instead of only focusing on defining the characteristics of the seafloor's bedrock and sediment, we are next eager to map the nodules themselves," he said.

Seabed mining

The majority of marine mining activities remain limited to shallow waters (sand, silt, construction mud), whereas deep-sea mining (200 meters or more) has become an issue of international controversy. The prospect of polymetallic nodule mining has generated the most excitement.

The argument against the seabed mining is that the ecosystems of the seafloor and the potential impacts of mining are still poorly understood. For example, the majority of the organisms in polymetallic nodule fields resides either on the nodules themselves or in the sediment immediately beneath them. Nodule mining could result in habitat changes and the direct extinction of some benthic organisms.

A growing number of countries and companies have already called for deep sea mining plans to be suspended "until and unless" there is clear scientific evidence that it can be conducted safely and the marine environment is protected by international regulations, The Guardian reported.

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